If the iPhone 4 is no longer committed to a contractual 2 year agreement, AT&T will remove their carrier lock from it for you. Just call them up or open a chat session with their support on their website and ask them if they can unlock your iPhone 4 for you.

Once it is unlock, I think just about any GSM 3g SIM card will work.

As far as where to get a good international SIM card I'm not really sure.

Get the iPhone 5 unlocked in ebay. There are several users now offering IMEI unlock (basically, they are requesting the unlock through the official AT&T channels, probably employees) for 5 USD. Recommended user is unlock_fusion, with more than 80K positive feeddback (that's crazy).This is permanent. Then you go to France, and buy the equivalent of a pay as you go network. You will not get LTE with your AT&T iPhone 5, but you will be able to get 3G.

Get the iPhone 5 unlocked in ebay. There are several users now offering IMEI unlock (basically, they are requesting the unlock through the official AT&T channels, probably employees) for 5 USD. Recommended user is unlock_fusion, with more than 80K positive feeddback (that's crazy).This is permanent. Then you go to France, and buy the equivalent of a pay as you go network. You will not get LTE with your AT&T iPhone 5, but you will be able to get 3G.

Awesome. That is the route I am going to go unless a jailbreak and then unlock comes out that I can do myself.

Now, I just need to find out which sim cards I can use over 9 days between 2 months.

Awesome. That is the route I am going to go unless a jailbreak and then unlock comes out that I can do myself.

Now, I just need to find out which sim cards I can use over 9 days between 2 months.

I would take that route regardless if there is a jailbreak, unlock. This is 100% secure and your phone gets factory unlocked forever, you can restore, update, etc and it will retain its unlock. I would do this ASAP as there is always the possibility the could take down that user. No modification is required to software or hardware to the iPhone, you just provide your IMEI, they enter it in the Apple Database, and it is unlocked.